The invention relates to a level control system for vehicles having air springs. Such a level control system is known, for example, from DE 35 42 975 A1.
Modern motor vehicles have many safety systems of which each takes up space in the motor vehicle so that space is tightly measured. For this reason, the effort is great to configure even necessary components of the motor vehicle as compact as possible. Accordingly, for example, in the recent past, it has been suggested that the spare tire of a motor vehicle be configured as a folding tire which is basically not filled with compressed air and is, instead, only filled or inflated as required. According to statutory requirements which are present in some countries, the full pressure in the folding wheel has to be reached within a certain time span in the case of need.
The compressor of the level control system of the motor vehicle can be used for pumping of the folding wheel. It has, however, been shown that the pregiven time span, within which the folding wheel must be pumped up, can only be maintained by accepting a long compressor running time and a high compressor temperature. If at the start of pumping up, the compressor temperature is already increased, for example, because of an increased ambient temperature, or the folding wheel has a large air volume (as is the case, for example, in off-road vehicles), it can happen that the compressor becomes destroyed during the fill-up operation of the folding wheel because of overheating.
It is a task of the invention to provide a level control system with which filling up or inflating a spare ti e is possible within a short time span without the compressor becoming greatly heated or destroyed.
As a controllable valve which switches the check valve, the following is to be understood: the check valve lies in a pressurized air line and the controllable valve lies in an additional pressurized air line which branches off from the first pressurized air line ahead of the check valve and is returned again to the additional pressurized air line rearward of the check valve. The check valve lies in the first pressurized air line. With the controllable valve, the additional pressurized air line can be switched clear (then the check valve is bridged) in one switching state or be blocked in another switching state.
An advantage of the invention is that the spare wheel can be filled with the aid of the compressor as well as wit the aid of the compressed air reservoir. If the temperature at he compressor is above a limit value ahead of the fill-up operation or exceeds the limit value during the fill-up operation, then the fill-up operation is carried out or is continued exclusively by the compressed air reservoir (the temperature of the compressor is monitored by the control unit of the level control system in a manner known per se). In this way, an overheating or a destruction of the compressor cannot occur because of the fill-up operation and the limited fill-up time can be maintained even for large spare wheels. A further advantage of the invention is that during the filling up of the spare wheel with the aid of the compressor, the compressed air is not conducted via he air dryer of the level control system. This advantage of the invention will be understood when one considers the following: the air, which is transferred from the compressor into the spare wheel, is taken from the level control system because the spare wheel is decoupled from the level control system after the fill-up operation and is used on the motor vehicle. If the pare wheel is filled up with the aid of the compressor via the air dryer. then the air dryer becomes moist and has to be regenerated. Since, for the regeneration, the air in the spare wheel is no longer available because the air is taken from the level control system (and not discharged from the spare wheel via the air dryer into the atmosphere), the regeneration of this moisture must take place with the aid of the remaining air in the level control system. It has been shown that the air, which is available in the level control system, is not sufficient for a satisfactory regeneration especially when the spare wheel has a large air volume. A further advantage of the invention is that, during a fill-up operation of the spare wheel, the compressor s well as the compressed air reservoir are not connected to the atmosphere. For this reason, the compressor and the compressed air reservoir pump exclusively into the spare wheel and a xe2x80x9clost pumpingxe2x80x9d into the atmosphere does not occur.